Dual electrochemical catalysis of Bi2Mo3O12/Ti cathode for hydrogen peroxide production in electro-Fenton system

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Enhanced electro-Fenton degradation of tetracycline in aqueous solution using a self-supported BiOCl/CF cathode

The cathode material is critical to the yield of hydrogen peroxide (H₂O₂) and electro-Fenton (EF) performance. In this work, bismuth oxychloride (BiOCl) as one of the representatives of ternary oxides was grown in situ on carbon felt (CF) through a simple solvothermal method and employed directly as a self-standing cathode for the EF degradation of the target contaminant tetracycline (TC). TC can be almost completely degraded, up to 95% in 90 min under the heterogeneous EF process. The characterizations demonstrated that the BiOCl/CF electrode exhibited excellent conductivity due to CF as the supporting carbon material with a 3D network structure; meanwhile, this hybrid electrode also possessed abundant active sites attributed to the decorated BiOCl having rich oxygen defects. Finally, the rational reaction mechanism of TC was also elucidated by the X-ray photoelectron spectroscopy (XPS) spectrum, free radical quenching experiments and electron paramagnetic resonance (EPR) spectra, in which hydroxyl radicals (ċ OH) were considered as the dominant active oxidants and BiOCl had a synergistic effect on in-situ generation and decomposition of H₂O₂.

One-step preparation of Co2V2O7: synthesis and application as Fenton-like catalyst in gas diffusion electrode

Bimetallic oxides and MOFs have been employed as catalysts for ORR via two-electron and Fenton-based processes. This work reports the development of a new green one-step route for obtaining Co2V2O7....

Facile synthesize of CdS QDs decorated Bi2MoO6/Bi2Mo3O12 heterojunction photocatalysts and enhanced performance of visible light removal of organic pollutants

In this work, the CdS quantum dots (QDs) decorated Bi₂MoO₆/Bi₂Mo₃O₁₂ (BMO) heterojunction photocatalyst (C/BMO) has been successfully synthesized using a facile two-step hydrothermal method. The as-prepared photocatalysts were characterized by XRD, FTIR, XPS, FESEM, TEM, UV-vis DRS, PL and photoelectrochemical measurements to investigate the effects of CdS(QDs) and BMO heterojunction on the structure, morphology, optical and charge carrier transmission characteristics of the photocatalysts. Narrow band gap and superior catalytic activities were found in C/BMO as compared with pure BMO. Moreover, the C/BMO photocatalyst containing twice CdS content (2-C/BMO) exhibits even higher photocatalytic activity and stability. After exposure to visible light for 30 min, the degradation rate of Rhodamine B (RhB), Methylene blue (MB) and Ofloxacin (OFX) by 2-C/BMO reached 95%, 92% and 76%, respectively. Radicals scavenging experiments and electron spin-resonance spectroscopy (ESR) investigations indicated that the superoxide radical anions (∙O2- ), hole (h⁺) and hydroxyl radicals (•OH) are the dominating active species in the photodegradation processes. ∙O2- and h⁺ are the key factors in the degradation of RhB and OFX solutions, and •OH is the major determinant in removal of MB. The process and photocatalytic mechanism on 2-C/BMO was discussed. Well absorption of visible light, effective separation of photoelectron-hole pairs and the transportation of photogenerated carriers at the interfaces of ternary semiconductor heterojunction are suggested as the key factors to enhance the photocatalytic performance of the photocatalysts.

Carbonaceous cathode materials for electro-Fenton technology: Mechanism, kinetics, recent advances, opportunities and challenges

Electro-Fenton (EF) technique has gained significant attention in recent years owing to its high efficiency and environmental compatibility for the degradation of organic pollutants and contaminants of emerging concern (CECs). The efficiency of an EF reaction relies primarily on the formation of hydrogen peroxide (H₂O₂) via 2e^─ oxygen reduction reaction (ORR) and the generation of hydroxyl radicals (^●OH). This could be achieved through an efficient cathode material which operates over a wide pH range (pH 3-9). Herein, the current progresses on the advancements of carbonaceous cathode materials for EF reactions are comprehensively reviewed. The insights of various materials such as, activated carbon fibres (ACFs), carbon/graphite felt (CF/GF), carbon nanotubes (CNTs), graphene, carbon aerogels (CAs), ordered mesoporous carbon (OMCs), etc. are discussed inclusively. Transition metals and hetero atoms were used as dopants to enhance the efficiency of homogeneous and heterogeneous EF reactions. Iron-functionalized cathodes widened the working pH window (pH 1-9) and limited the energy consumption. The mechanism, reactor configuration, and kinetic models, are explained. Techno economic analysis of the EF reaction revealed that the anode and the raw materials contributed significantly to the overall cost. It is concluded that most reactions follow pseudo-first order kinetics and rotating cathodes provide the best H₂O₂ production efficiency in lab scale. The challenges, future prospects and commercialization of EF reaction for wastewater treatment are also discussed.

Fit-for-purpose treatment goals for produced waters in shale oil and gas fields

Hydraulic fracturing (HF), or "fracking," is the driving force behind the "shale gas revolution," completely transforming the United States energy industry over the last two decades. HF requires that 4-6 million gallons per well (15,000-23,000 m³/well) of water be pumped underground to stimulate the release of entrapped hydrocarbons from unconventional (i.e., shale or carbonate) formations. Estimated U.S. produced water volumes exceed 150 billion gallons/year across the industry from unconventional wells alone and are projected to grow for at least another two decades. Concerns over the environmental impact from accidental or incidental release of produced water from HF wells ("U-PW"), along with evolving regulatory and economic drivers, has spurred great interest in technological innovation to enhance U-PW recycling and reuse. In this review, we analyze U-PW quantity and composition based on the latest U.S. Geographical Survey data, identify key contamination metrics useful in tracking water quality improvement in the context of HF operations, and suggest "fit-for-purpose treatment" to enhance cost-effective regulatory compliance, water recovery/reuse, and resource valorization. Drawing on industrial practice and technoeconomic constraints, we further assess the challenges associated with U-PW treatment for onshore U.S. operations. Presented are opportunities for targeted end-uses of treated U-PW. We highlight emerging technologies that may enhance cost-effective U-PW management as HF activities grow and evolve in the coming decades.